Deposition of copper with increased adhesion

ABSTRACT

A method and apparatus for improving the adhesion of a copper layer to an underlying layer on a wafer. The layer of copper is formed over a layer of material on a wafer and the copper layer impacted with ions to improve its adhesion to the underlying layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed toward the field of manufacturingintegrated circuits.

2. Description of the Related Art

Presently, aluminum is widely employed in integrated circuits as aninterconnect, such as plugs and wires. However, higher device densities,faster operating frequencies, and larger die sizes have created a needfor a metal with lower resistivity than aluminum to be used ininterconnect structures. The lower resistivity of copper makes it anattractive candidate for replacing aluminum.

One challenge in employing copper instead of aluminum is the fact thatcopper dry etching is not presently feasible. A polishing process, suchas chemical mechanical polishing, is used to remove undesirable portionsof a deposited layer of copper. The need to use chemical mechanicalpolishing presents a challenge, because copper has poor adhesion tomaterials that are presently being used as diffusion barriers beneaththe copper. The polishing of copper that is deposited over a diffusionbarrier can therefore result in portions of the copper being undesirablypeeled away from the surface of the diffusion barrier. This can renderan integrated circuit defective.

When depositing copper, it is desirable to employ chemical vapordeposition (“CVD”), as opposed physical vapor deposition, because CVDprovides for a more conformal layer of copper. However, the chemicalvapor deposition of copper presents a further challenge. The challengearises from a byproduct that is produced during the deposition of thecopper.

In one instance, the chemical vapor deposition of copper is achieved byusing a precursor known as Cupraselect, which has the formula Cu(hfac)L.The L represents a Lewis base compound, such as vinyltrimethylsilane(“VTMS”). The (hfac) represents hexafluoroacetylacetonato, and Curepresents copper. During the CVD of copper using the Cu(hfac)Lprecursor, the precursor is vaporized and flowed into a depositionchamber containing a wafer. In the chamber, the precursor is infusedwith thermal energy at the wafer's surface, and the following reactionresults:

2 Cu(hfac)L→Cu+Cu(hfac)₂+2L  (Eqn. 1)

The resulting copper (Cu) deposits on the upper surface of the wafer,along with the Cu(hfac)₂ byproduct. The gaseous Lewis base byproduct(2L) is purged from the chamber. The presence of the byproduct as wellas other contaminants on the wafer's surface reduces the adhesion of thecopper to an underlying diffusion barrier, such as tantalum nitride.

In order to improve the adhesion of copper to an underlying diffusionbarrier, the process for depositing copper has been divided into twosteps. During a first step, physical vapor deposition (PVD) is performedto deposit a seed layer of copper. In PVD, a copper target is placedabove a substrate onto which the copper is to be deposited. An argon gasis introduced into the environment between the copper target and thesubstrate. The argon gas is then excited through the use of a radiofrequency (“RF”) signal to create a plasma containing ions.

The ions from the plasma strike the copper target, thereby dislodgingparticles of the copper which deposit on the substrate. These copperparticles are generally ionized and thus are highly energetic. Suchenergetic copper ions adhere well to the barrier layers. The substrateis biased so that a voltage gradient forms between the target and thesubstrate, thereby causing the copper ions to accelerate along thegradient and bombard the substrate. As a result of the bombardment, thecopper particles strongly adhere to the surface of the substrate.Secondly, this PVD process provides a clean interface between the copperseed layer and the barrier layer.

Once the seed layer of copper is deposited using PVD, a bulk layer ofcopper is deposited. The bulk layer is deposited by either standardchemical vapor deposition or electrical plating. The bulk layer ofcopper adheres relatively well to the copper seed layer.

However, the use of the PVD process results in poor step coverage, whichis unacceptable for devices that have small features. Further, the PVDprocess cannot be accomplished in the same chamber as either chemicalvapor deposition or electrical plating. The need to have both a PVDchamber and either a CVD or electrical plating chamber increasesintegrated circuit manufacturing costs.

Accordingly, it is desirable to provide for the conformal chemical vapordeposition of copper onto a diffusion barrier, so that the adhesionbetween the copper and underlying diffusion barrier is improved. It isalso desirable for such a deposition to be performed in a single chamber(in situ). It is further desirable to decrease the production ofcontaminant byproducts during the deposition of copper, so that thedeposition can be performed faster and with a smaller amount ofprecursor.

SUMMARY OF THE INVENTION

In accordance with the present invention, a layer of material, such ascopper, is formed on the surface of a wafer with improved adhesion. Informing the layer of copper, a copper seed layer is first deposited on asurface of the wafer. Once the seed layer is deposited, the copper isbombarded (annealed) with ions to improve the adhesion of the copper tothe surface of the wafer.

More specifically, ions in a plasma of an inert gas bombard the copperto provide the improved adhesion, which results in the copper being“mounted” on the surface of the wafer. This mounting increases theadhesion of the copper to the wafer's surface. Additionally, suchbombardment flattens the copper grains to improve charge mobility. Theplasma is generated in one embodiment of the present invention using aninert gas, such as argon. Alternatively, hydrogen can be employed alongwith an inert gas to generate a plasma for bombarding the copper as wellas providing for contaminant removal. The addition of the hydrogenprovides for the removal of copper deposition byproducts such as carbon,oxygen, fluorine and the like, thereby enhancing the adhesion of thecopper to the barrier layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the present invention are explained with the help ofthe attached drawings in which:

FIG. 1 illustrates a sequence of operations that are performed fordepositing a layer of copper in accordance with the present invention;

FIGS. 2(a)-2(d) illustrate the deposition of a layer of copper inaccordance with the present invention;

FIG. 3 illustrates a deposition chamber that is used in the depositionof copper in accordance with the present invention; and

FIG. 4 illustrates a control system that is employed in accordance withthe present invention to control the operation of a deposition chamberthat is used for depositing copper in accordance with the presentinvention.

DETAILED DESCRIPTION

FIG. 1 illustrates a sequence of operations for depositing copper on thesurface of a wafer in accordance with the present invention. First, aseed layer of copper is deposited on the upper surface of the wafer instep 100. The seed layer of copper is deposited using chemical vapordeposition and can be deposited as either a continuous or discontinuouslayer of copper. In accordance with the present invention, a Cu(hfac)Lprecursor is employed in the deposition of the seed layer. However,other copper precursors in combination with reducing agents could beused to form the seed layer, e.g., Cu⁺²(hfac)L precursor with a hydrogenreducing agent.

Once the seed layer of copper is deposited, in step 101, the seed layeris treated with a plasma. The plasma is generated by applying RF energyto one or more gases. In one embodiment of the present invention, theplasma gas is composed of only a single gas, such as argon, krypton orxenon. In an alternate embodiment of the present invention, the gaseousmixture includes multiple gases, such as a combination of argon andhydrogen; krypton and hydrogen; or xenon and hydrogen.

During plasma treatment, the substrate onto which the copper has beendeposited acquires a bias. The bias results in ions in the plasma beingaccelerated toward the substrate. These ions impact the copper seedlayer, thereby causing the copper to adhere to the surface of thesubstrate, i.e., the copper grains become “mounted” on the substrate andalso flattens the grains to improve charge mobility. This enhances theadhesion of the copper seed layer to the substrate. Also, if hydrogenions are present in the plasma, they combine with precursor contaminantbyproducts and are removed from the chamber.

Once the plasma treatment is completed in step 101, a bulk deposition ofcopper is performed in step 102. The copper deposited during the bulkdeposition is deposited over the plasma treated copper to form a layerof copper having a desired thickness and improved adhesion to thewafer's surface. The bulk deposition is achieved using a chemical vapordeposition with Cu(hfac)L or some other bulk copper deposition process.

It one embodiment of the present invention, the copper seed layerdeposition, plasma treatment, and bulk deposition are accomplished in asingle chamber that is capable of performing both chemical vapordeposition and plasma treatment. Accordingly, the layer of copper isformed completely in situ. In further embodiments of the presentinvention, the chemical vapor depositions and plasma treatment areperformed in different chambers.

FIGS. 2(a)-2(d) illustrate the formation of a layer of copper in anintegrated circuit in accordance with the present invention. FIG. 2(a)shows a via 116 that has been formed (i.e., etched) in a layer 111 ofinsulative material, such as silicon dioxide. The layer 111 ofinsulative material overlies a substrate 110 which is to be electricallycoupled to other elements in the integrated circuit. The substrate 110is to be coupled to the other elements by an interconnect structure thatwill be formed within the via 116.

The upper surface of the insulative layer 111 of material and the uppersurface of the substrate 110 that is within the perimeter of the via 116are overlain by a diffusion barrier 112. The diffusion barrier 112 isemployed to inhibit the diffusion of interconnect structure metal intothe substrate 110. In one embodiment of the present invention, theinterconnect structure metal is copper, and the diffusion barrier is arefractory metal or refractory metal nitride. For example, therefractory metal nitride is preferably tantalum nitride, but may also betitanium nitride, tantalum, tungsten nitride or another suitablematerial that functions as a diffusion barrier between the metal (e.g.,copper) and the substrate 110.

FIG. 2(b) illustrates the deposition of a seed layer 113 of copper whichis to be employed in an interconnect structure. The seed layer of copper113 is deposited on the upper surface of the diffusion barrier 112 usingchemical vapor deposition. In one embodiment of the present invention,as shown in FIG. 2(b), the seed layer 113 of copper is deposited to bediscontinuous, i.e., there are gaps between deposition regions. In analternate embodiment (not shown) the seed layer 113 of copper isdeposited to be continuous with a thickness in a range of 10 Å to 300 Å.The thickness of the seed layer depends upon the plasma treatmentparameters used to treat the seed layer. Thus, the thickness of thedeposition should conform to the chosen treatment parameters.

The chemical vapor deposition of the seed layer 113 is preferablyachieved using the Cu(hfac)L precursor, with L being VTMS. LiquidCu(hfac)L is vaporized and flowed into the environment containing thediffusion barrier 112. Vaporization of the precursor can be accomplishedby “bubbling” nitrogen or hydrogen through the liquid precursor. Thevaporized precursor is provided to the environment at a flow rate ofapproximately 0.1 to 1 SCCM. The environment is controlled so that ithas a pressure in the range of 0.5 mTorr to 1.5 mTorr, and thetemperature of the substrate is in a range of 150 to 250° C. Thedeposition process is carried out for a time period in the range of 30seconds to 5 minutes depending upon the desired thickness of the seedlayer. The seed layer may be chemically deposited using other copperprecursors such as Cu⁺² (hfac)₂ with a hydrogen reducing agent. Broadlyspeaking, any form of copper deposition is considered to be within thescope of the invention.

Once the seed layer of copper 113 is deposited, it is treated with aplasma 114, as shown in FIG. 2(c). In accordance with the presentinvention, the plasma 114 is formed by providing energy to one or moregases, i.e., a gaseous mixture, that includes an inert gas with anatomic mass that is similar to the atomic mass of copper. Such gasesinclude argon, xenon and krypton. In one embodiment of the presentinvention, the gaseous mixture is composed of argon.

When argon is employed, an argon gas is flowed into the environmentcontaining the seed layer of copper 113 at a flow rate in the range of100 to 500 sccm. The argon gas is transformed into a plasma by infusingit with energy from a RF signal having a frequency in the range of 100kHz—20 MHz, where 13.56 MHz has been found to produce sufficienttreatment results using a RF power level in the range of 100 watts to2000 watts. Generally speaking, the higher the power that is applied tothe plasma the better the treatment of the seed layer. The resultingplasma 114 is maintained for a time period in the range of 10 to 60seconds.

When performing the plasma treatment, the environment of the seed layerof copper 113 is controlled so that the pressure is in a range of 0.1 to1.5 Torr, and the temperature of the substrate 110 is set to be in arange of 150 to 250° C.

As the plasma 114 is formed, the argon becomes ionized. The resultingions of argon accelerate towards and impact the seed layer 113 ofcopper. The impact from the ions causes the impacted copper layer 113 tohave improved bonding with the diffusion barrier 112. This “mounting” ofthe copper material on the diffusion barrier 112 improves the adhesionof the copper seed layer 113 to the diffusion barrier 112.

In an alternate embodiment of the present invention, the plasma 114 isformed from a gaseous mixture that is a mixture of hydrogen with aninert gas, such as argon, krypton or xenon. When argon is employed, theratio of argon to hydrogen is in a range of 1:1 to 3:1. The plasma isformed from the gaseous mixture of argon and hydrogen by providingenergy to the gas in the same manner as forming a plasma of only argon.

As described above, the chemical vapor deposition of copper using theCu(hfac)L precursor results in the deposition of copper along with acontaminant (hfac) byproduct. This contaminant byproduct adverselyaffects the adhesion of the copper 113 to the diffusion barrier 112. Theaddition of the hydrogen to the plasma 114 results in the elimination ofa portion of (hfac) byproduct as well as other contaminants such asfluorine, oxygen, and/or carbon.

When the argon-hydrogen plasma 114 is employed, the argon ions impactthe copper 113, as described above, and the hydrogen combines with(hfac) byproduct according to the following equation:

H₂+(hfac)→2H(hfac)  (Eqn. 2)

The 2H(hfac) is a gaseous byproduct of the reaction and is exhaustedfrom the environment in which the seed layer 113 is deposited. As aresult of the employing the argonhydrogen plasma 114, the adhesion ofthe seed layer 113 to the diffusion barrier 112 is improved by twomechanisms. The first mechanism is the bombardment of the copper by theargon ions to improve the bond between the copper and the diffusionbarrier 112. The second mechanism is the elimination of (hfac)contaminant byproduct and/or other contaminants that will bond withhydrogen and be removed from the chambers.

In alternate embodiments of the present invention, the plasma 114 may befurther altered, while still achieving the benefit of improving theadhesion between the copper seed layer 113 and underlying diffusionbarrier 112. For example, other inert gases, such as krypton and xenon,can be substituted for the argon in the plasma 114. Such substitutionsmay be made whether or not hydrogen is employed. Further, the plasma 114may be composed of only hydrogen. In such an embodiment, improvedadhesion between the copper seed layer 113 and the diffusion barrier 112results from the elimination of (hfac) byproduct and other contaminantsthat may interfere with copper bonding.

Once the seed layer of copper 113 is treated with the plasma 114, a bulkdeposition of copper is performed to form the final copper layer 115having a desired thickness. As shown in FIG. 2(d), the newly depositedcopper is deposited using chemical vapor deposition and merges with(grows upon) the seed layer of copper 113 to form the final layer ofcopper 115. In a preferred embodiment of the invention, the bulk CVD ofcopper layer 115 is achieved as described above with respect to FIG.2(b) using the Cu(hfac)L precursor; however, other bulk depositionprocesses may be used such as Cu⁺²(hfac)_(z) with a hydrogen reducingagent.

The bulk deposition of copper is accomplished until the final layer 115of copper has a thickness in a range of 1000 Å to 1 micron. Since thenewly deposited copper is deposited on top of the seed layer 113, whichhas improved adhesion to the underlying diffusion barrier 112, theadhesion of the final layer of copper 115 to the diffusion barrier 112is also improved. As a result of the improved adhesion, the copper isless likely to be undesirably peeled away from the diffusion barrier 112during polishing.

FIG. 3 illustrates a CVD system 120 that can be employed to form a layerof copper in accordance with the present invention. The chamber is amodel WxZ chamber manufactured by Applied Materials, Inc. of SantaClara, Calif., that has been modified to perform copper deposition inaccordance with the invention. The system 120 includes a process chamber137 in which copper deposition and plasma treatment is performed.Included in the process chamber 137 are a wafer support 130 forsupporting a wafer and a showerhead 129 for flowing reactant gases intothe process chamber 137.

The process chamber 137 is defined by a set of walls 131 that areelectrically and thermally isolated from the wafer support 130 andshowerhead 129 by isolators 132. For providing thermal energy, the wafersupport 130 includes a resistive coil (not shown) that provides heat tothe wafer support's surface. For providing the energy for forming aplasma, the showerhead 129 is coupled to a signal source 126 thatprovides signals having frequencies in a range of 100 kHz to 20 MHz.Both the processing chamber walls 131 and the wafer support 130 arecoupled to ground.

A pressure control unit 135, e.g., a vacuum pump, is coupled to theprocess chamber 137 for setting the pressure in the process chamber 137.The pressure control unit 135 also provides for purging reactantbyproducts from the process chamber.

In order to provide reactants to the process chamber 137, the system 120also includes a mixer block 127, vaporizer 128, gas panel 121, andliquid panel 122. The gas panel 121 provides gaseous reactants and iscoupled to both the vaporizer 128 and the mixer block 127. The liquidpanel 122 provides liquid reactants and is coupled to the vaporizer 128.

The vaporizer 128 provides for converting liquid reactants into gaseousreactants. When a liquid reactant is employed, the liquid panel 122provides the liquid reactant to the vaporizer 128, and the vaporizer 128vaporizes the liquid and uses an inert dilutant gas such as helium,hydrogen, nitrogen or argon as a carrier gas. Alternatively, thevaporizer may produce a gaseous reactant through evaporation. When bothgaseous and liquid reactants are employed, the gas panel 121 providesthe vaporizer 128 with the gaseous reactants, and the liquid panel 122provides the vaporizer 128 with the liquid reactants. The vaporizer thenprovides for the combination and vaporization of these reactants. Themixer block 127 is coupled to pass gaseous reactants from the gas panel121 and vaporizer 128 to the showerhead 129.

The formation of the layer of copper is carried out in situ in a singleprocessing system such as that shown in FIG. 3. A wafer 140 containingan upper surface on which copper is to be deposited is placed in theprocess chamber 137 on wafer support 130, which is spaced approximately350 mils from a showerhead 129. In one embodiment of the presentinvention, the upper surface of the wafer 140 is a diffusion barrierthat is formed by a refractory metal nitride, such as titanium nitride,tantalum nitride or tungsten nitride. The wafer (substrate) is thenprocessed as described above.

The above-described process steps (FIGS. 2(a) through 2(d)) for forminga layer of copper can be performed in a system that is controlled by aprocessor based control unit. FIG. 4 shows a control unit 200 that canbe employed in such a capacity. The control unit includes a processorunit 205, a memory 210, a mass storage device 220, an input control unit270, and a display unit 250 which are all coupled to a control unit bus225.

The processor unit 205 is either a microprocessor or other engine thatis capable of executing instructions stored in a memory. The memory 210can be comprised of a hard disk drive, random access memory (“RAM”),read only memory (“ROM”), a combination of RAM and ROM, or anotherprocessor readable storage medium. The memory 210 contains instructionsthat the processor unit 205 executes to facilitate the performance ofthe above mentioned process steps. The instructions in the memory 210are in the form of program code. The program code may conform to any oneof a number of different programming languages. For example, the programcode can be written in C+, C++, BASIC, Pascal, or a number of otherlanguages.

The mass storage device 220 stores data and instructions and retrievesdata and program code instructions from a processor readable storagemedium, such as a magnetic disk or magnetic tape. For example, the massstorage device 220 can be a hard disk drive, floppy disk drive, tapedrive, or optical disk drive. The mass storage device 220 stores andretrieves the instructions in response to directions that it receivesfrom the processor unit 205. Data and program code instructions that arestored and retrieved by the mass storage device 220 are employed by theprocessor unit 205 for performing the above mentioned process steps. Thedata and program code instructions are first retrieved by the massstorage device 220 from a medium and then transferred to the memory 210for use by the processor unit 205.

The display unit 250 provides information to a chamber operator in theform of graphical displays and alphanumeric characters under control ofthe processor unit 205. The input control unit 270 couples a data inputdevice, such as a keyboard, mouse, or light pen, to the control unit 200to provide for the receipt of a chamber operator's inputs.

The control unit bus 225 provides for the transfer of data and controlsignals between all of the devices that are coupled to the control unitbus 225. Although the control unit bus is displayed as a single bus thatdirectly connects the devices in the control unit 200, the control unitbus 225 can also be a collection of busses. For example, the displayunit 250, input control unit 270 and mass storage device 220 can becoupled to an input-output peripheral bus, while the processor unit 205and memory 210 are coupled to a local processor bus. The local processorbus and input-output peripheral bus are coupled together to form thecontrol unit bus 225.

The control unit 200 is coupled to the elements of the chamber in FIG. 3that are employed in forming a layer of copper in accordance with thepresent invention. Each of these elements is coupled to the control unitbus 225 to facilitate communication between the control unit 200 and theelement. These elements include the following: the gas panel 121, theliquid panel 122, a heating element 230, such as the resistive coil (notshown)in the wafer support, the pressure control unit 135, the signalsource 126, the vaporizer 128, and the mixer block 127. The control unit200 provides signals to the chamber elements that cause the elements toperform the operations described above for the process steps of forminga layer of copper.

In operation, the processor unit 205 directs the operation of thechamber elements in response to the program code instructions that itretrieves from the memory 210. In response to these instructions, thechamber elements are directed to perform the process steps describedabove with reference to FIG. 1.

Once a wafer is placed in the processing chamber, a seed layer of copperis deposited on the wafer in step 100 (FIG. 1). In order to perform thedeposition in step 100, the processor unit 205 executes instructionsretrieved from the memory 210. The execution of these instructionsresults in the elements of the chamber being operated to deposit a layerof material on a substrate as described above with reference to FIG.2(b).

Once the seed layer of copper is deposited, instructions retrieved fromthe memory 210 instruct the processor unit 205 to cause the elements ofthe chamber 120 to perform a plasma treatment in step 101. The executionof these instructions results in the elements of the chamber 120 beingoperated to treat the deposited copper with a plasma as described abovewith reference to FIG. 2(c).

Once the plasma treatment is completed, instructions retrieved from thememory 210 instruct the processor unit 205 to cause the elements of thechamber 120 to perform a bulk deposition of copper in step 102. Theexecution of these instructions results in the elements of the chamber120 being operated to perform a bulk deposition to treat the copper asdescribed above with reference to FIG. 2(d).

Although the present invention has been described in terms of specificexemplary embodiments, it will be appreciated that various modificationsand alterations might be made by those skilled in the art withoutdeparting from the spirit and scope of the invention as specified by thefollowing claims.

What is claimed is:
 1. A method of processing a substrate comprising thesteps of: (a) chemical vapor depositing a seed layer consistingessentially of copper upon said substrate; and (b) after said step (a),treating the copper seed layer through ion bombardment to cause thecopper seed layer to adhere to an upper surface of the substrate.
 2. Themethod of claim 1, wherein said step (b) includes the step of: forming aplasma, wherein the plasma includes ions that bombard the copper seedlayer.
 3. The method of claim 1 wherein said copper seed layer isdeposited in a continuous layer.
 4. The method of claim 1 wherein saidcopper seed layer is deposited in a discontinuous layer.
 5. The methodof claim 1, wherein the substrate contains a diffusion barrier.
 6. Themethod of claim 5, wherein the diffusion barrier is composed of arefractory metal, or refractory metal nitride.
 7. The method of claim 6,wherein the diffusion barrier is a material selected from a groupconsisting of tantalum, titanium nitride, tantalum nitride, and tungstennitride.
 8. The method of claim 2, wherein the plasma is formed using aninert gas.
 9. The method of claim 8, wherein the inert gas is one ormore gases selected from a group consisting of argon, krypton, andxenon.
 10. The method of claim 8 wherein the inert gas is combined withhydrogen.
 11. The method of claim 1, further including the step of: (c)depositing additional copper upon the copper seed layer deposited insaid step (a) and treated in said step (b).
 12. The method of claim 11,wherein said additional copper deposited in said step (c) combines withsaid copper seed layer deposited in said step (a) to form a continuouslayer of copper.
 13. The method of claim 12, wherein steps (a), (b) and(c) are all performed in a processing chamber, and the substrate is notremoved from the processing chamber until said steps (a), (b) and (c)have all been completed.
 14. The method of claim 1, wherein said step(a) is performed using chemical vapor deposition.
 15. The method ofclaim 14, wherein the chemical vapor deposition is accomplished using achemical compound having a formula of Cu(hfac)L; where Cu representscopper, hfac represents hexafluoroacetylacetonato, and L represents aLewis base compound.
 16. The method of claim 2, wherein the plasma isformed using hydrogen.
 17. A method for forming a layer of copper over alayer of material on a wafer, said method comprising the steps of: (a)placing the wafer in a processing chamber; (b) chemical vapor depositinga seed layer consisting essentially of copper on the layer of material,while the wafer is in the processing chamber; and (c) after said step(b), treating the copper seed layer through ion bombardment to cause thecopper seed layer to adhere to an upper surface of the layer ofmaterial, while the wafer is in the processing chamber.
 18. The methodof claim 17, wherein said step (c) includes the step of: forming aplasma, wherein the plasma includes ions that impact the copper seedlayer.
 19. The method of claim 18, wherein the plasma is formed usinghydrogen.
 20. The method of claim 17, wherein the layer of material is adiffusion barrier.
 21. The method of claim 18, wherein the plasma isformed using a gaseous mixture that includes an inert gas.
 22. Themethod of claim 21, wherein the inert gas is a gas selected from a groupconsisting of argon, krypton, and xenon.
 23. The method of claim 21,wherein the gaseous mixture includes at least one gas selected from agroup consisting of argon, krypton, xenon, and hydrogen.
 24. The methodof claim 17, further including the step of: (d) depositing additionalcopper on the copper seed layer treated in said step (c), while thewafer is in the processing chamber.
 25. The method of claim 24, whereinsaid step (d) is performed using chemical vapor deposition.
 26. Themethod of claim 25, wherein the chemical vapor deposition isaccomplished using a chemical compound having a formula of Cu(hfac)L;where Cu represents copper, hfac represents hexafluoroacetylacetonato.and L represents a Lewis base compound.